Merseyside is experiencing the biggest measles outbreak the north of England
has seen in decades, with more than 200 people already confirmed with the
disease.

Cases have jumped by more than 50 per cent in a single month, with children under five worst affected.

Public health experts said the low uptake of the measles, mumps and rubella (MMR) vaccine since it was wrongly linked with autism in 1998 had set the scene for the "very infectious disease" to take hold once more.

The Health Protection Agency said there had been 210 laboratory confirmed cases on Merseyside since the start of the year, while it was also investigating another 92 "probable" cases.

By comparison, at the end of March there were 123 confirmed cases and 66 probables.

An HPA spokesman said: "Thirty-nine were ill enough to need in-patient treatment in hospital. Thankfully, all have either recovered or are recovering."

Just under a quarter (46) of cases have been in those under a year - too young to have been offered the MMR jab, and therefore totally unprotected. Eleven of those 46 infants had to be admitted to hospital. Almost half of all cases were in under fives.

Measles is often thought of as a relatively minor infection, and in most people illness is confined to fever and a rash for about a week.

However, it causes complications in about one in 15. According to the advice website Patient UK, "of all childhood infections, it is the one most likely to cause the complication of encephalitis (inflammation of the brain), sometimes resulting in brain damage".

"It can also cause convulsions, ear infections, bronchitis and pneumonia, which can lead to long-term lung problems."

Liverpool is at the heart of the outbreak, with 125 confirmed cases, while there have also been 29 in the suburb of Knowsley, 22 in Sefton, 11 in Cheshire and seven in Wirral. There have been others in Halton, St Helens and Warrington.

Dr Roberto Vivancos, an HPA consultant, said: "It’s obvious from these statistics that people who are not fully vaccinated are not just at risk themselves, but they pose an infection risk to others, such as defenceless babies and toddlers who are too young to be vaccinated.

“Measles is a very infectious illness that spreads rapidly amongst children and adults who are not protected by MMR vaccine.

"It is also a serious illness that can lead to serious complications. On rare occasions, people die from measles.

"It should not be treated lightly, but it is an avoidable illness and we strongly advise parents to ensure that their children are vaccinated."

Recent outbreaks are the result of years of depressed MMR vaccination rates, which dropped sharply after 1998, when Andrew Wakefield published his flawed paper in The Lancet linking MMR with autism.

Measle cases have surged to levels not seen since the MMR vaccine was introduced in 1988.

The peak year so far was 2008 - a whole decade after the Lancet article - with 1,370 confirmed cases across England and Wales.

The biggest outbreaks have been in London, with 664 that year and 440 in 2007, partially due to its large population, and partially because vaccination rates dropped further in the capital than most other areas.

However, they are still below the recommended rate of 95 per cent, which is required to produce an effect called 'herd immunity', in which the few not vaccinated are protected because the virus cannot pass from person to person in the community.

Kim Mulholland, professor of child health and vaccinology at the London School of Hygiene & Tropical Medicine, said: "The current outbreak of measles in the Merseyside area is a timely reminder that Britain, like other European countries, remains susceptible to measles outbreaks.

"Over half of the 200-plus cases were under five years of age, which is not surprising given that more than 10 per cent of British children under five are not vaccinated against measles.

"This provides more than enough susceptible children to sustain outbreaks, which will continue while immunisation coverage is inadequate and measles continues to circulate in other parts of the world."